1. Field of the Invention
This invention relates to a user-propelled vehicle or wheelchair. More particularly, it relates to a wheelchair propelled by push levers connected to drive wheels through bicycle chains and variable ratio rear gear clusters.
2. Description of the Prior Art
Most wheelchair users have little or no functional use of their lower extremities, but have preserved normal upper body function. Accordingly, the conventional wheelchair requires the user to propel the chair by repetitively pushing on push-rims attached to the main wheels of the chair. The arm and shoulder motions that are required are undesirable because they utilize the small, relatively weak, muscles of the rotator cuff and ultimately lead to stress injury and degenerative arthritis of the shoulder joint. This is also an inefficient means of locomotion; providing only a one-to-one ratio of distance traveled for distanced pushed. It is, however, an ubiquitous and relatively simple machine that can be easily maintained. Several attempts have been made to improve on this standard with very limited success.
Several inventions employ the use of levers for the user to propel the chair. This is an improvement because it makes use of the larger and more powerful triceps and pectoral muscles, with reduced shoulder stress. Still, however, all of these devices have fallen short of success.
For example, U.S. Pat. No. 4,865,344 provides only one speed having one fixed gear ratio, and thereby forgoes the significant mechanical advantage gained by using a set of multiple gear ratios This machine also requires the user to steer with hand levers attached to the push levers, increasing the complexity of steering and propulsion movements.
U.S. Pat. No. 5,322,312 is another attempt to propel a wheelchair with a push lever. It also lacks sufficient mechanical advantage, having only one gear ratio. The use of a detachable skateboard device makes this machine unnecessarily complex, expensive, and difficult to maintain.
U.S. Pat. 5,209,506 is cumbersome in requiring the user to steer with handlebars which are simultaneously pushed and pulled to propel the chair. The linkage required to operate this machine is also too complex for easy care, and the position of the steering/push lever obstructs easy entry and exit of the chair.
U.S. Pat. No. 4,811,964 also uses push levers for power, but in a rowing motion. This machine would be difficult to steer, having a combined row-steer motion; it also has only one speed, and uses a complex system of pulleys and linkage, all of which serve to make it impractical.
U.S. Pat. No. 3,994,509 is another lever-driven machine that makes use of a very complex and expensive system of forward and reverse clutches. It also provides only a single forward speed, and has a very wide profile, to accommodate the wide-set wheels.
There are several inventions that use a set of bicycle pedals to turn a crank which, in turn, transfers power via a bicycle chain to either front or rear wheels. All of these hand-crank designs suffer from the fact that the hand cranking motion is extremely fatiguing. Further, they are too big and too heavy. The cranking/steering device obstructs entry and exit. These wheelchairs generally lack multiple gears and are difficult to steer while cranking. U.S. Pat. No. 4,720,117 is a typical example of this type of machine.
U.S. Pat. No. 5,362,081 is an attempt to adapt the mechanical advantage of multiple gear ratios to the standard wheelchair format. It does not, however, save the user from the repetitive motion injury and degenerative damage to the shoulder joints; and, in requiring the use of the user's smaller, weaker rotator cuff muscles, it is more fatiguing than a push lever driven machine. This particular model also requires the user to let go of the steering/drive wheel to shift gears.